Zero-Sequence Circulating Current Suppression for Parallel T-Type Three-Level inverters

In common DC-bus two parallel T-type three-level inverter systems, the neutral-point (NP) potential balancing and the zero-sequence circulating current (ZSCC) should be considered in practical applications. The differences of the parallel inverters in parameters, such as the filters, reference output current, and the unsynchronized switching states, will produce the ZSCC. However, the parameters and NP potential influence the amplitude of the ZSCC. In this paper, the modeling of NP potential and ZSCC in T-type three-level parallel inverter system is established and analyzed. In order to balance the NP potential, the compensation control based on the zero-sequence voltage injection and feed-back control is proposed. The combination of the compensation control and CM voltage injection is adopted to suppress the ZSCC. Finally, the effectiveness of the proposed strategy is verified by the simulation results.